The present invention relates to an image forming apparatus of an electrophotographic method wherein residual toner on an image carrier is removed by a brush and a cleaning blade.
In recent years, image forming apparatuses of an electrophotographic method are introduced in many offices. In the image forming apparatus of an electrophotographic method, a latent image formed on a photoreceptor (image carrier) is visualized, thus, a toner image on a photoreceptor is transferred onto a sheet or onto an intermediate transfer member. On the photoreceptor from which images have been transferred, there remains toner that has not been transferred. Therefore, the residual toner is removed by a brush or a cleaning blade.
However, there are sometimes occasions where toner on the photoreceptor cannot be removed even by a brush and a cleaning blade, and if the toner and its additive which have failed to be removed continue sticking on the photoreceptor, a stuck matter grows greater while image forming is continued, resulting in a main cause for occurrence of image defect.
A technology described in Unexamined Japanese Patent Application Publication No. 10-254323 is one to change a difference between a linear velocity on a surface of a photoreceptor and a linear velocity on an outer circumference of a brush roller, at least once during a period of time from the start of rotation of the photoreceptor to its stop. This technology can suppress an increase of sticking toner, and prevent image defect.
Incidentally, in the image forming apparatus wherein residual toner on a photoreceptor is removed by using both a brush and a cleaning blade, when images having a high image area rate are printed continuously, a large amount of toners stick to the brush, and the brush turns out to be under the condition that it contains toner. When the brush turns out to be under the condition to contain toner, toner and its additive move from the brush to the photoreceptor, depending on electric potential of the photoreceptor that faces the brush, and the toner and its additive stick to the photoreceptor undesirably. After the toner and its additive have stuck to the photoreceptor once, toner and its additive further stick beginning from the stuck toner serving as the starting point, and stuck matter grows greater, when printing for a long time (as shown in FIG. 4, stuck matter α such as toner on photoreceptor 410 has a shape of a raindrop, and a large stuck matter sometimes grows up to 5 mm or more although a size of small stuck matter α is about 10 μm that cannot be confirmed visually). As a result, stuck matters cause an occurrence of image defect that a part of a halftone image and a part of a solid image are lost.
However, in the technology described in Unexamined Japanese Patent Application Publication No. 10-254323, it is not possible to suppress sufficiently the stuck matters generated through the circumstances.